Semiconductor device wiring and interconnect structure is formed by layering various materials on a wafer in a prescribed pattern. Popular methods for depositing material layers include physical vapor deposition, chemical vapor deposition and the like. While these techniques produce stable material layers when deposited on an underlying wafer, material that deposits on other surfaces within the deposition chamber tends to flake or crumble as the deposition chamber thermally cycles, particularly when a significant amount of material has accumulated thereon. Such flaking or crumbling may cause wafer contamination. Accordingly, in order to reduce this type of contamination, chamber surfaces must be periodically coated with a pasting layer which prevents flaking and crumbling of the deposited material, as described below.
One of the most widely used deposition techniques (especially popular for electrical interconnect formation) is sputtering deposition. To deposit a film of material within a sputtering deposition chamber, a target of material to be deposited and a wafer (on which target material is to be deposited) are mounted within the chamber. A gas is flowed into the chamber and a negative voltage is applied to the target with respect to the chamber walls so as to excite the gas into a plasma state. As ions from the plasma bombard the target, energy is transferred from the energetic ions to the target, causing target particles to leave the target, travel in linear trajectories and deposit on the wafer.
As stated previously, sputtering deposition is often used for forming electrical interconnects within and between semiconductor devices formed on a wafer. One of the most popular interconnect materials is titanium-nitride because of its conductivity and diffusion-barrier properties. Unfortunately, titanium-nitride is brittle and when deposited alone can flake from chamber surfaces during thermal cycling. This flaking may contaminate an underlying wafer.
To prevent flaking, a pasting layer of titanium is often deposited over the titanium-nitride layer. The titanium layer bonds more tightly than titanium-nitride, and effectively glues underlying titanium-nitride layers in place on the chamber surfaces. Such titanium pasting layers are periodically deposited (e.g., every 25 wafers) on chamber surfaces to prevent deposited titanium-nitride layers from flaking therefrom. Pasting layers are most often deposited on non-production objects such as a dummy wafer or on the deposition chamber's shutter.
While pasting layers successfully reduce flaking and extend the processing time between required chamber cleaning and/or replacement of chamber parts (e.g., shields, pedestals, shutters, collimators and clamp rings), within a high density plasma deposition chamber the first production wafer processed following a pasting step (i.e., the first wafer) exhibits markedly different deposited film characteristics than the deposited film characteristics of subsequently processed production wafers (i.e., the first wafer effect occurs). Accordingly, the first wafer must be discarded.
A need therefore exists for an improved pasting process for use within a high density plasma deposition chamber that will not result in the first wafer effect.